1. Field of the Invention
The present invention relates to an ad hoc network, a node, a routing control method and a routing control program for an ad hoc network configured of a plurality of nodes.
2. Description of the Related Art
In recent years, development and wide spread of mobile communication terminals have been increasing interest in a mobile ad hoc network. The mobile ad hoc network is a network dynamically constructed among mobile communication terminals. The mobile ad hoc network is a network that does not depend on a base station and core network, which are indispensable in a conventional mobile radio communication network, and autonomously constructed by mobile communication terminals.
Expected applied examples include a sensor network, communications during disaster, communications between automobiles, a personal area network, a home network, a temporal network in an event, and a network for information exchanges. In such a communication environment, demands may rise for new types of application implementations such as a service allowing a mobile terminal such as a mobile phone to utilize devices scattered around the terminal, a service operated by a plurality of devices existing in different networks in collaboration and coordination with each other, and the like.
A reactive-type Dynamic Source Routing (DSR), a proactive-type Optimized Link State Routing (OLSR) and the like have been proposed as a routing protocol for a mobile ad hoc network.
The reactive-type DSR is also called an on-demand and type, and starts a route finding process to a communication partner at a starting time of data transmission. This process is terminated when a route is founded, or when examinations of all available route patterns are completed. Once a route is found and established, the route is maintained until it becomes impossible to communicate with the partner therethrough, or until the route itself becomes unnecessary. Since route finding starts after a request to start data transmission is made, communication packets do not generate load on a network when data communication is not performed. On the other hand, some slight delay occurs from when a request to start data transmission is made until data is actually transmitted to a communication partner. In addition, since the route finding process continues until a route is found, or until examinations of all available route patterns are completed, this reactive-type DSR has a disadvantage of producing overheads when finding a communication partner fails.
The proactive-type OLSR is also called a table drive type, and a proactive-type routing protocol standardized by the Internet Engineering Task Force (IETF) is Topology Broadcast Based on Reverse-Path Forwarding (TBRPF). Each node has a table for storing information on routing from the node to other nodes on a network. In response to changes in a network topology, each node updates the routing information in its own table, and ensures consistency between the network topology and the routing information. Since the routing information is periodically exchanged between nodes, a delay does not occur from when a request to start to transmit data is made until the data is actually transmitted to a communication partner. However, since nodes communicate with each other even while not transmitting data, a communication load is placed on the network. Heretofore, how to reduce such a communication load has been studied while examining the frequency of updating routing information and a range of nodes involved in updating routing information. However, the frequency and the range of nodes have a trade-off with efficiency and convenience.
A mobile ad hoc network may include a sensor without power supply, and such a sensor and a mobile terminal have limitations in memory and processing performance. Accordingly, there is a need for a protocol that achieves reduction in overheads at times of transmission and non-transmission of data, and decrease in consumption of CPU resources and the like in a sensor and a mobile terminal.
To be more precise, an achievement of reduction in overheads and delay at the time of data transmission is necessary for a reactive type routing protocol. On the other hand, achievements of reduction in communications traffic between nodes at a time of non-transmission of data, and reduction in an information volume (routing information, etc.) held in each node are desired for a proactive type routing protocol.